Zeta Positive Hydrogenated Nanodiamond Powder, Zetapositive Single Digit Hydrogenated Nanodiamond Dispersion, and Methods for Producing the Same

ABSTRACT

The present invention relates to a method for producing zeta positive hydrogenated nanodiamond particles, and to a method for producing zeta positive single digit hydrogenated nanodiamond dispersions. The present invention further relates to zeta positive hydrogenated nanodiamond powder and zeta positive single digit hydrogenated nanodiamond dispersion.

PRIORITY

This application is a continuation application of U.S. Ser. No.14/893942 filed on Nov. 25, 2015, claiming priority of internationalapplication PCT/FI2014/050434 filed on May 30, 2014 and Finnish nationalapplication FI20135605 filed on May 31, 2013, the contents all of whichare incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a method for producing zeta positivehydrogenated nanodiamond powder and zeta positive single digithydrogenated nanodiamond dispersion. The present invention furtherrelates to zeta positive hydrogenated nanodiamond powder and zetapositive single digit hydrogenated nanodiamond dispersion.

BACKGROUND ART

Nanodiamond (ND) also referred to as ultrananocrystalline diamond orultradispersed diamond (UDD) is a unique nanomaterial which can easilybe produced in hundreds of kilograms by detonation synthesis.

Detonation nanodiamonds (ND) were first synthesized by researchers fromthe USSR in 1963 by explosive decomposition of high-explosive mixtureswith negative oxygen balance in a non-oxidizing medium. A typicalexplosive mixture is a mixture of trinitrotoluene (TNT) and hexogen(RDX) and a preferred weight ratio of TNT/RDX is 40/60.

As a result of the detonation synthesis a diamond-bearing soot alsoreferred to as detonation blend is obtained. This blend comprisesnanodiamond particles, which typically have an average particle size ofabout 2 to 8 nm, and different kinds of non-diamond carbon contaminatedby metals and metal oxide particles coming from the material of thedetonation chamber. The content of nanodiamonds in the detonation blendis typically between 30 and 75% by weight.

The nanodiamond-containing blends obtained from the detonation containsame hard agglomerates, typically having a diameter of above 1 mm. Suchagglomerates are difficult to break. Additionally the particle sizedistribution of the blend is very broad.

The diamond carbon comprises spa carbon and the non-diamond carbonmainly comprises sp² carbon species, for example carbon onion, carbonfullerene shell, amorphous carbon, graphitic carbon or any combinationthereof.

There are number of processes for the purification of the detonationblends. The purification stage is considered to be the most complicatedand expensive stage in the production of nanodiamonds.

For isolating the end diamond-bearing product, a complex of chemicaloperations directed at either dissolving or gasifying the impuritiespresent in the material are used. The impurities, as a rule, are of twokinds: non-carbon (metal oxides, salts etc.) and nondiamond forms ofcarbon (graphite, black, amorphous carbon).

Chemical purification techniques are based on the different stability ofthe diamond and non-diamond forms of carbon to oxidants. Liquid-phaseoxidants offer an advantage over gas or solid systems, because theyallow one to obtain higher reactant concentrations in the reaction zoneand, therefore, provide high reaction rates.

In the recent years nanodiamonds have received more and more attentiondue to several existing applications within electroplating (bothelectrolytic and electroless), polishing, various polymer mechanical andthermal composites, CVD-seeding, oils and lubricant additives as well aspossible new applications such as luminescence imaging, drug delivery,quantum engineering etc.

The fact that the available nanodiamond materials possess a variety ofvarious surface functions and thus agglomeration (from several hundredsof nanometers to several microns), is effectively limiting their use inindustrial applications. As applying agglomerating nanodiamond grades,very high filler loadings are typically required, making their costefficient use impossible in most of the applications today. Moreover,nanodiamond agglomeration is effectively limiting or prohibiting theoptimization of various application end product technical properties.Agglomeration is making it impossible to use nanodiamonds inapplications wherein the product optical properties have to be retained;agglomeration is causing scratching in polishing and fine-polishingapplications; agglomeration can have a direct adverse effect on polymercomposite mechanical properties; agglomeration in an electroplatingelectrolyte or electroless deposition chemicals (due to non-optimalnanodiamond zeta potential as in relation to electrolyte pH regime)makes their usage impossible or economically ineffective formanufacturing mechanically improved metal coatings; agglomeration iseffectively prohibiting nanodiamond usage as a drug carrier material;agglomeration is having an adverse effect on CVD produced diamond filmquality etc.

Cost efficient and technologically optimized usage of nanodiamondmaterials both in their powder, suspension and dispersion form can onlybe achieved if nanodiamonds are substantially mono-functionalized typeand have thus, depending on the type of surface modification, thehighest possible affinity to various solvents and polymer, metal orceramic materials. Such a substantially mono-functionalized nanodiamondpossesses, depending on the type of surface functionalization, either ahighly positive or negative zeta potential value.

The significance of zeta potential is that its value can be related tothe stability of colloidal dispersions. The zeta potential indicates thedegree of repulsion between adjacent, similarly charged particles indispersion or suspension. For molecules and particles that are smallenough, a high zeta potential will confer stability, i.e., the solutionor dispersion will resist aggregation. When the potential is low,attraction exceeds repulsion and the dispersion will break andflocculate. Therefore, colloids with high zeta potential (negative orpositive) are electrically stabilized while colloids with low zetapotentials tend to coagulate or flocculate. If the zeta potential is 0to ±5 mV, the colloid is subjected to rapid coagulation or flocculation.Zeta potential values ranging from ±10 mV to ±30 mV indicate incipientinstability of the colloid (dispersion), values ranging from ±30 mV to±40 mV indicate moderate stability, values ranging from ±40 mV to ±60 mVgood stability as excellent stability is reached only with zetapotentials more than ±60 mV.

Several methods for functionalizing the nanodiamonds with differentfunctional groups have been developed. Typical functionalizednanodiamonds are hydrogenated nanodiamonds, carboxylated nanodiamondsand hydroxylated nanodiamonds, but contain still a mixture of typicallyoppositely charged functions and thus, mediocre zeta potential valuesand are thus not available in their solvent dispersion forms.

Publication A. Krueger and D. Lang, Adv. Funct. Mater. 2012, 22, 890-906discloses methods for hydrogenating nanodiamonds by applying hydrogengas at elevated temperature. These methods, however, have disadvantages.For example, in addition to formation of C—H bonds, an increase in theamount of OH-groups is observed.

The publication A. Krueger and D. Lang, Adv. Funct. Mater. 2012, 22,890-906 further discloses methods to produce hydrogenated nanodiamondsin different types of plasma reactors.

US 2012/0315212 A1 discloses a method for obtaining hydrogenated diamondparticles from aggregate structures which contain diamond particles withan average particle diameter of less than 10 nm. The aggregatestructures are heated under a gas atmosphere such that the diamondparticles are obtained from the aggregate structures. It is essentialthat the aggregate structures are heated under a gas atmosphere which,in terms of reactive gases, contains hydrogen gas in a proportion of atleast 80%. Most preferably the diamond particles are heated in a purehydrogen gas atmosphere. The heating under the gas atmosphere occurspreferably at a pressure of 10 mbar. The obtained diamond particles showzeta potential exceeding +30 mV at a pH range from 3 to 7. Preferablythe obtained nanodiamond particles are dispersed in deionized water.

Based on above disclosure, there is a qualitative and quantitative needfor an efficient method for producing zeta positive hydrogenatednanodiamond powder and highly zeta positive single digit hydrogenatednanodiamond dispersions.

SUMMARY OF THE INVENTION

The present invention relates to a method for producing zeta positivehydrogenated nanodiamond powder according to claim 1.

The present invention further relates to a method for producing zetapositive single digit hydrogenated nanodiamond dispersion according toclaim 7.

The present invention further relates to zeta positive hydrogenatednanodiamond powder according to claim 20.

The present invention further relates to zeta positive single digithydrogenated nanodiamond dispersion according to claim 23.

It has now been surprisingly found that by heating nanodiamond particlesat substantially ambient pressure under a gas atmosphere comprisinghydrogen gas highly zeta positive hydrogenated nanodiamond powder can beproduced. As the process is conducted without using pressurizedconditions, the method of the present invention is safer, scalable andmore economic compared to those methods where pressurized conditions arerequired.

It was also surprisingly found that by using one or more inert gaseswith hydrogen gas in the gas atmosphere, smaller concentration ofhydrogen gas is needed to produce the highly zeta positive hydrogenatednanodiamond powder. Hydrogen gas concentration from 1 to 10% issufficient for the method of the present invention. As the hydrogen gasconcentration is low, the process itself is safer and more costeffective.

It was also surprisingly found that by further treating the zetapositive hydrogenated nanodiamond powder produced with the method of thepresent invention highly zeta positive single digit hydrogenatednanodiamond dispersions can be produced. The produced zeta positivehydrogenated nanodiamond powder can be dispersed into several liquidmediums to obtain highly zeta positive single digit hydrogenatednanodiamond dispersions.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 shows sample (samples A, B, C and D) positions and gas flowdirection in a furnace according to the present invention.

FIG. 2 shows the temperature plot for nanodiamond hydrogenation processconducted at 500° C. for 6 hours' time according to the presentinvention.

FIG. 3a shows untreated nanodiamond powder B samples.

FIG. 3b shows hydrogenated nanodiamond B samples according to thepresent invention.

FIG. 4 shows zeta potential of hydrogenated nanodiamond B powderaccording to the present invention made at 600° C. for 6 hours' time,after subjecting said sample for ultrasonic treatment in water for onehour time.

FIG. 5 shows particle size distribution of single digit hydrogenatednanodiamond dispersion after beads assisted sonic disintergrationprocess (BASD) according to the present invention.

FIG. 6 shows dispersion stability of single digit hydrogenatednanodiamond dispersion according to present invention.

FIG. 7 shows particle size distribution of single digit hydrogenatednanodiamond dispersion after beads assisted sonic disintergrationprocess according to the present invention.

FIG. 8 shows thermogravimetric analysis curve of dried hydrogenatednanodiamond dispersion according to the present invention.

FIG. 9 shows particle size distribution of single digit hydrogenatednanodiamond dispersion according to the present invention.

FIG. 10 shows particle size distribution of 2.0 wt. % single digithydrogenated nanodiamond dispersion according to the present invention.

FIG. 11 shows particle size distribution of 3.1 wt. % single digithydrogenated nanodiamond dispersion according to the present invention.

FIG. 12 shows particle size distribution of 3.0 wt. % single digithydrogenated nanodiamond dispersion according to the present invention.

FIG. 13 shows particle size distribution of 5.0 wt. % single digithydrogenated nanodiamond dispersion according to the present invention.

DETAILED DESCRIPTION

By term “zeta positive nanodiamond” is meant a nanodiamond particlehaving a positive zeta potential.

By term “hydrogenated nanodiamond” is meant a nanodiamond particlehaving hydrogen functions on its surface.

By term “zeta positive hydrogenated nanodiamond” is meant a nanodiamondparticle having hydrogen functions on its surface and having a positivezeta potential.

By term “zeta positive single digit hydrogenated nanodiamond” is meant ananodiamond particle substantially in its primary particle form (alsoreferred as to substantially in non-agglomerated form) having hydrogenfunctions on its surface and having a positive zeta potential.

By term “zeta positive single digit hydrogenated nanodiamond dispersion”is meant a dispersion of a liquid medium and nanodiamond particles wherethe nanodiamond particles are substantially present in their primaryparticle form and having hydrogen functions on theirs surface, and thedispersion having a positive zeta potential.

By particle size distribution D10 is meant that 10% of the particles aresmaller than given particle size, and 90% of particles are larger thangiven particle size.

By particle size distribution D50 is meant that 50% of the particles aresmaller than given particle size, and 50% of particles are larger thangiven particle size.

By particle size distribution D90 is meant that 90% of the particles aresmaller than given particle size, and 10% of particles are larger thangiven particle size.

Zeta potentials referred in this description relate to zeta potentialsmeasured in aqueous suspensions or dispersions.

In a first aspect of the present invention there is provided a methodfor producing zeta positive hydrogenated nanodiamond powder.

More particularly there is provided a method for producing zeta positivehydrogenated nanodiamond powder, the method comprising heatingnanodiamond particles under a gas atmosphere comprising hydrogen gas atsubstantially ambient pressure, wherein hydrogen gas content in the gasatmosphere is 1-10%.

The precursor nanodiamond particles for producing the zeta positivehydrogenated nanodiamond powder may be essentially pure nanodiamondparticles, preferably having a nanodiamond content of at least 87% byweight, more preferably at least 97% by weight. The nanodiamondparticles may contain graphite and amorphous carbon originating from theproduction of the nanodiamonds. They may also contain some residualmetal impurities, either as metals or in metal oxide form. Thenanodiamond particles used as precursors for the hydrogenatednanodiamonds are commercially available.

The gas atmosphere comprises hydrogen gas. In order to avoidinterferences during the heating process of the nanodiamond particlesunder the gas atmosphere by foreign substances preferably hydrogen gasis used with purity of at least 99.9%, more preferably at least,99.999%. The hydrogen gas may be cleaned prior to introduction into areaction chamber, for example, by via a palladium membrane. Hydrogen gasmay be fed periodically or continuously into the reaction chamber.Hydrogen gas is commercially available.

In a preferred embodiment the gas atmosphere comprises additionally oneor more inert gases. The inert gas can be any gas that is not chemicallyreactive. That is, the inert gas can be any gas that is not chemicallyreactive in the method of the present invention. Preferably the inertgas is selected from the group consisting of argon, nitrogen, helium, ora mixture thereof. Most preferably the inert gas is argon.

Preferably the heating of the nanodiamond particles under the gasatmosphere occurs in a reaction chamber with hydrogen gas and one ormore inert gases being continuously guided through the reaction chamberduring the heating. Hydrogen gas and one or more inert gases are guidedcontinuously, as a mixture, through the reaction chamber with flow ratefrom 0.01 to 20 slpm (standard liter per minute), preferably from 0.1 to15 slpm, and more preferably from 0.1 to 10 slpm.

Hydrogen gas content in the gas mixture guided through a reactionchamber is 1-10%, preferably 2-8%, and more preferably 3-7%. Thehydrogen gas content relates to hydrogen content in reactive gas flow.The percentage relates here to the percentage of particles.

The reaction chamber may be any suitable reactor, known by a skilledperson, which can be used in the present invention. The reaction chambermay be for example a suitable furnace.

The heating of the nanodiamond particles under the hydrogen comprisinggas atmosphere occurs substantially at ambient pressure. In oneembodiment the heating occurs at a pressure ranging from 5 mbar to 20bar, preferably from 5 mbar to 2 bar.

The nanodiamond particles are heated under the hydrogen comprising gasatmosphere from 1 to 15 hours, preferably from 2 to 10 hours, and morepreferably from 3 to 9 hours.

The nanodiamond particles are heated under the hydrogen comprising gasatmosphere at a temperature from 300 to 1000° C., preferably from 400 to900° C., and more preferably from 400 to 850° C.

The zeta positive hydrogenated nanodiamond powder obtained by theheating the nanodiamond particles under the gas atmosphere are initiallyin agglomerated powder form. If the agglomerated powder is subjected toone hour ultrasonic treatment, for example with Hielscher 400 Wultrasonic device, in water, average particle size distribution (D50) ofthe zeta positive hydrogenated nanodiamond particles in the agglomeratedform is from 2 nm to 400 nm, preferably from 2 nm to 100 nm. Forconducting said particle size distribution measurement, reliable andreproducible results can be received with nanodiamond concentrationsvarying between 0.1 to 1.5 wt-%.

As suspended into water, zeta potential of the obtained zeta positivehydrogenated nanodiamond particles is over +30 mV, preferably over +40mV, more preferably over +50 mV, and most preferably over +60 mV,measured at pH higher than 7.

As suspended into water, zeta potential of the obtained zeta positivehydrogenated nanodiamond particles is over +30 mV at a pH-range from 1.5to 13, preferably at a pH-range from 2 to 11, and more preferably at apH-range from 2 to 10.

In a second aspect of the present invention there is provided a methodfor producing zeta positive single digit hydrogenated nanodiamonddispersions.

More particularly, there is provided a method for producing zetapositive single digit hydrogenated nanodiamond dispersion, the methodcomprising

i) heating nanodiamond particles under a gas atmosphere comprisinghydrogen gas at substantially ambient pressure for producing zetapositive hydrogenated nanodiamond powder, wherein hydrogen gas contentin the gas atmosphere is 1-10%;

ii) suspending the zeta positive hydrogenated nanodiamond powder into aliquid medium; and

iii) subjecting the zeta positive hydrogenated nanodiamond suspension tobeads assisted sonic disintergration (BASD) process.

In step i) nanodiamond particles are heated under a gas atmosphere atsubstantially ambient pressure for producing zeta positive hydrogenatednanodiamond powder, wherein the gas atmosphere comprises hydrogen gas.

The precursor nanodiamond particles may be essentially pure nanodiamondparticles, preferably having a nanodiamond content of at least 87% byweight, more preferably at least 97% by weight. The nanodiamondparticles may contain graphite and amorphous carbon originating from theproduction of the nanodiamonds. They may also contain some residualmetal impurities, either as metals or in metal oxide form. Thenanodiamond particles used as precursors for the hydrogenatednanodiamonds are commercially available.

The gas atmosphere comprises hydrogen gas. In order to avoidinterferences during the heating process of the nanodiamond particlesunder the gas atmosphere by foreign substances preferably hydrogen gasis used with purity of at least 99.9%, more preferably at least,99.999%. The hydrogen gas may be cleaned prior to introduction into thereaction chamber, for example, by via a palladium membrane. Hydrogen gasmay be fed periodically or continuously into the reaction chamber.Hydrogen gas is commercially available.

In a preferred embodiment the gas atmosphere comprises additionally oneor more inert gases. The inert gas can be any gas that is not chemicallyreactive. That is, the inert gas can be any gas that is not chemicallyreactive in the method of the present invention. Preferably the inertgas is selected from the group consisting of argon, nitrogen, helium, ora mixture thereof. Most preferably the inert gas is argon.

Preferably the heating of the nanodiamond particles under the gasatmosphere occurs in a reaction chamber with hydrogen gas and one ormore inert gases being continuously guided through the reaction chamberduring the heating.

Hydrogen gas and one or more inert gases are guided continuously, as amixture, through the reaction chamber with flow rate from 0.01 to 50slpm (standard liter per minute), preferably from 0.1 to 15 slpm, andmore preferably from 0.1 to 10 slpm.

Hydrogen gas content in the gas mixture guided through a reactionchamber is 1-10%, preferably 2-8%, and more preferably 3-7%. Thehydrogen gas content relates to hydrogen content in reactive gas flow.The percentage relates here to the percentage of particles.

The reaction chamber may be any suitable reactor, known by a skilledperson, which can be used in the present invention. The reaction chambermay be for example a suitable furnace.

The heating of the nanodiamond particles under the hydrogen comprisinggas atmosphere occurs substantially at ambient pressure. In oneembodiment the heating occurs at a pressure ranging from 5 mbar to 20bar, preferably from 5 mbar to 2 bar.

The nanodiamond particles are heated under the hydrogen comprising gasatmosphere from 1 to 15 hours, preferably from 2 to 10 hours, and morepreferably from 3 to 9 hours.

The nanodiamond particles are heated under the hydrogen comprising gasatmosphere at a temperature from 300 to 1000° C., preferably from 400 to900° C., and more preferably from 400 to 850° C.

The zeta positive hydrogenated nanodiamond powder obtained by theheating the nanodiamond particles under the gas atmosphere are initiallyin agglomerated powder form.

In step ii) the obtained zeta positive hydrogenated nanodiamond powderis suspended into a liquid medium.

Any known suitable methods and devices may be used for suspending thezeta positive hydrogenated nanodiamond powder into a liquid medium.Examples of such methods are magnetic stirring, ultrasound, combinedmagnetic stirring and ultrasound treatment, magnetic stirring followedby ultrasound treatment, or magnetic stirring followed by ultrasoundtreatment followed by magnetic stirring.

The zeta positive hydrogenated nanodiamond particles may be in thesuspension in agglomerated form, or as a mixture of agglomerated andsingle digit form. Particle size distribution of the agglomeratedsuspension form is between 2 nm to 400 nm, preferably between 2 nm and100 nm.

The liquid medium may be any suitable liquid medium. The liquid mediumis preferably selected from the group consisting of polar proticsolvents, polar aprotic solvents, dipolar aprotic solvents, aromaticsolvents, chlorinated solvents, ionic liquids, or a mixture of any saidmediums.

Preferred polar protic solvents are water; alcohols such as methanol,ethanol, iso-propanol, butanol, linear aliphatic diols such as ethyleneglycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,1,8-octanediol; branched diols such as 1,2-propanediol, 1,3-butanediol,2,3-butanediol, 1,3-butanediol, 1,2-pentanediol, etohexadiol,p-menthane-3,8-diol, 2-methyl-2,4-pentanediol; and carboxylic acids suchas formic acid and acetic acid.

Preferred polar aprotic solvents are tetrahydrofuran, propylenecarbonate and lactams such as N-methyl-2-pyrrolidone (NMP) andN-ethyl-2-pyrrolidone (NEP).

Preferred dipolar aprotic solvents are ketones such as acetone andmethyl ethyl ketone (MEK); esters such as methyl acetate, ethyl acetate;N,N-methyl-formamide and dimethyl sulfoxide (DMSO).

Preferred aromatic solvents are toluene, xylenes and benzene.

Preferred chlorinated solvents are dichloromethane, trichloroethyleneand chloroform.

Preferred ionic liquids are 1-ethyl-3-methylmidazolium chloride,1-butyl-3-methylmidazolium chloride, 1-ethyl-3-methyl-imidazoliumethylsulfate, 1-ethyl-3-methyl imidazolium diethylphosphate,1-ethyl-3-methyl-imidazolium dicyanamide,Tris-(2-hydroxyethyl)-methylammonium methylsulfate,1-ethyl-3-methyl-imidazolium thiocyanate, 1-ethyl-3-methyl-imidazoliumtetrafluoroborate, 1-ethyl-3-methyl-imidazoliumtrifluoromethanesulfonate, 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methyl-imidazoliummethylcarbonate and 1-butyl-3-methyl-imidazolium methylcarbonate, Themost preferred ionic liquids are 1-ethyl-3-methylmidazolium chloride and1-butyl-3-methylmidazolium chloride.

Preferably the liquid medium is selected from the group consisting ofwater, methanol, ethanol, iso-propanol, linear aliphatic diols, brancheddiols, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP) anddimethyl sulfoxide (DMSO), or a mixture of any said solvents. Morepreferably the solvent is selected from the group consisting of water,NMP, NEP, γ-butyrolactone and ethylene glycol, or a mixture of any saidsolvents. Even more preferably the solvent is selected from the groupconsisting of water, NMP, NEP and γ-butyrolactone, or a mixture of anysaid solvents.

Most preferably the liquid medium is water. The water may be deionized.

The zeta positive hydrogenated nanodiamond powder can be suspendeddirectly into water or other liquid mediums. Alternatively, the zetapositive hydrogenated nanodiamond powder can be first suspended intowater, then mixing another liquid medium, having boiling point abovewater and at least partly soluble in water, with the aqueous zetapositive hydrogenated nanodiamond suspension, and then distilling(evaporating) the water out, giving zeta positive hydrogenatednanodiamond particles suspended in the liquid medium other than water.

In step iii), the zeta positive hydrogenated nanodiamond suspension issubjected to beads assisted sonic disintergration (BASD) process forobtaining the zeta positive single digit hydrogenated nanodiamonddispersion.

The BASD process means combined beads milling and ultrasonicationprocesses. That is, the zeta positive hydrogenated nanodiamondsuspension is simultaneously beads milled and treated withultrasonication The beads mill devices and the ultrasonic devices, andthe BASD process are known for a skilled person. The beads assistedsonic disintergration process can be operated with pass orre-circulation method. In the pass method the material is fed to theapparatus at one end and discharged at the other end. In there-circulation method the material circulates in the system untilrequired particle size is obtained. The smaller the grinding mediaparticles are, the smaller is the particle size of the final product. Agrinding chamber of the apparatus can also be filled with an inertshield gas, such as nitrogen, that does not react with the materialbeing ground, to prevent oxidation or explosive reactions that couldoccur with ambient air inside the mill. The ultrasonication can be kepton during the whole milling or switched off at any stage, and optionallyswitched on again. The BASD process is run until a suitable particlesize is obtained. The apparatuses for the beads assisted sonicdisintergration are commercially available.

The obtained zeta positive hydrogenated nanodiamond particles in thedispersion are substantially in a single digit form.

In an embodiment of the present invention, after the BASD processobtained aqueous zeta positive single digit hydrogenated nanodiamonddispersion is further treated. Liquid medium other than water havingboiling point above water and at least partly soluble in water, is mixedwith the aqueous zeta positive single digit hydrogenated nanodiamonddispersion, following distillation of water, giving zeta positive singledigit hydrogenated nanodiamond particles dispersed in the liquid mediumother than water.

Zeta potential of the zeta positive single digit hydrogenatednanodiamond dispersion is over +35 mV, preferably over +40 mV, and mostpreferably over +50 mV measured at pH higher than 7.

Zeta potential of the zeta positive single digit hydrogenatednanodiamond dispersion is over +50 mV, preferably over +60 mV measuredat pH lower than or 7.

The zeta positive single digit hydrogenated nanodiamond dispersion isstable when the zeta potential is over +35 mV measured at pH higher than7.

D90 average particle size distribution of the zeta positive single digithydrogenated nanodiamond dispersion is from 2 nm to 30 nm, preferablyfrom 2 nm to 20 nm, more preferably from 2 to 14 nm, and most preferablyfrom 3 nm to 12 nm.

The zeta positive single digit hydrogenated nanodiamond particleconcentration in the dispersion is at least 0.2 wt-%, preferably between0.2 and 10 wt-%, and more preferably between 0.5 and 8 wt-%.

pH of the zeta positive single digit hydrogenated nanodiamond dispersionmay be basic, neutral or acidic. Preferably the pH is from 1.5 to 13,more preferably from 1.5 to 12, and most preferably from 2 to 10.

In a third aspect of the present invention there is provided zetapositive hydrogenated nanodiamond powder.

More particularly there is provided zeta positive hydrogenatednanodiamond powder comprising zeta positive hydrogenated nanodiamondparticles, wherein

i) zeta potential of the zeta positive hydrogenated nanodiamondparticles as suspended in water is over +30 mV measured at pH higherthan 7,

ii) D50 average particle size distribution of the zeta positivehydrogenated nanodiamond particles in the agglomerated form is from 2 nmto 400 nm, preferably from 2 nm to 100 nm when subjected to one hourultrasonic treatment in water.

Preferably the zeta potential of the zeta positive hydrogenatednanodiamond particles, as suspended in water, is over +40 mV, morepreferably over +50 mV, and most preferably over +60 mV measured at pHhigher than 7.

As suspended in water, zeta potential of the obtained zeta positivehydrogenated nanodiamond particles is over +30 mV at a pH-range from 1.5to 13, preferably at a pH-range from 2 to 11, and more preferably at apH-range from 2 to 10.

In a fourth aspect of the present invention there is provided a zetapositive single digit hydrogenated nanodiamond dispersion comprisingzeta positive single digit hydrogenated nanodiamond particles and aliquid medium.

More particularly there is provided zeta positive single digithydrogenated nanodiamond dispersion comprising zeta positive singledigit hydrogenated nanodiamond particles and a liquid medium, wherein

i) zeta potential of the zeta positive single digit hydrogenatednanodiamond dispersion is over +30 mV measured at pH higher than 7,

ii) D90 average particle size distribution of the zeta positive singledigit hydrogenated nanodiamond particles in the dispersion is from 2 nmto 12 nm.

The liquid medium may be any suitable liquid medium. The liquid mediumis preferably selected from the group consisting of polar proticsolvents, polar aprotic solvents, dipolar aprotic solvents, aromaticsolvents, chlorinated solvents, ionic liquids, or a mixture of any saidmediums.

Preferred polar protic solvents are water; alcohols such as methanol,ethanol, iso-propanol, butanol, linear aliphatic diols such as ethyleneglycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,1,8-octanediol; branched diols such as 1,2-propanediol, 1,3-butanediol,2,3-butanediol, 1,3-butanediol, 1,2-pentanediol, etohexadiol,p-menthane-3,8-diol, 2-methyl-2,4-pentanediol; and carboxylic acids suchas formic acid and acetic acid.

Preferred polar aprotic solvents are tetrahydrofuran, propylenecarbonate and lactams such as N-methyl-2-pyrrolidone (NMP) andN-ethyl-2-pyrrolidone (NEP).

Preferred dipolar aprotic solvents are ketones such as acetone andmethyl ethyl ketone (MEK); esters such as methyl acetate, ethyl acetate;N,N-methylformamide and dimethyl sulfoxide (DMSO).

Preferred aromatic solvents are toluene, xylenes and benzene.

Preferred chlorinated solvents are dichloromethane, trichloroethyleneand chloroform.

Preferred ionic liquids are 1-ethyl-3-methylmidazolium chloride,1-butyl-3-methylmidazolium chloride, 1-ethyl-3-methyl-imidazoliumethylsulfate, 1-ethyl-3-methyl imidazolium diethylphosphate,1-ethyl-3-methyl-imidazolium dicyanamide,Tris-(2-hydroxyethyl)-methylammonium methylsulfate,1-ethyl-3-methyl-imidazolium thiocyanate, 1-ethyl-3-methyl-imidazoliumtetrafluoroborate, 1-ethyl-3-methyl-imidazoliumtrifluoromethanesulfonate, 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methyl-imidazoliummethylcarbonate and 1-butyl-3-methyl-imidazolium methylcarbonate, Themost preferred ionic liquids are 1-ethyl-3-methylmidazolium chloride and1-butyl-3-methylmidazolium chloride.

Preferably the liquid medium is selected from the group consisting ofwater, methanol, ethanol, iso-propanol, linear aliphatic diols, brancheddiols, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP) anddimethyl sulfoxide (DMSO), or a mixture of any said solvents. Morepreferably the solvent is selected from the group consisting of water,NMP, NEP, γ-butyrolactone and ethylene glycol, or a mixture of any saidsolvents. Even more preferably the solvent is selected from the groupconsisting of water, NMP, NEP and γ-butyrolactone, or a mixture of anysaid solvents.

Most preferably the liquid medium is water. The water may be deionized.

Preferably the zeta potential of the zeta positive single digithydrogenated nanodiamond dispersion is over +40 mV, more preferably over+50 mV, and most preferably over +60 mV measured at pH higher than 7.

In an embodiment the zeta potential of the zeta positive single digithydrogenated nanodiamond dispersion is over +60 mV, and preferably over+70 mV measured at pH lower than or 7.

Concentration of the zeta negative single digit carboxylated nanodiamondparticles in the dispersion is at least 0.2 wt %, preferably between 0.2and 10 wt-%, and more preferably between 0.5 and 8 wt-%.

D90 average particle size distribution of the zeta positive single digithydrogenated nanodiamond particles is preferably from 3 nm to 12 nm.

pH of the zeta positive single digit hydrogenated nanodiamond dispersionmay be basic, neutral or acidic. Preferably the pH is from 1.5 to 13,more preferably from 1.5 to 12, and most preferably from 2 to 10.

In the following the invention will be described in more detail by meansof examples. The purpose of the examples is not to restrict the scope ofthe claims.

EXAMPLES

The following examples are according to the present invention.

Apparatuses and Materials

Ultrasonic device: Hielscher UP400S (from company Hielscher).

Beads mill device: Bühler PML2 (from company Bühler GmbH, Germany).

Particle size and zeta potential measurement tool: Malvern ZetasizerNanoZS.

The product zeta potential values were measured of samples diluted to0.1 wt-%. The product particle size distributions were measured ofsamples diluted to 0.5 wt-%.

Furnace (reaction chamber):

-   -   6-zone horizontal tubular furnace (6zHTF):        -   4 crucibles, 100 ml loading in each, 99.7% Al₂O₃        -   Gas change in single step—for the first very careful pumping            vacuum down to 10⁻¹ mbar and then introducing gas,        -   During treatment gas flow was 200 ml/min.

Nanodiamond powders:

-   -   uDiamond® Molto nanodiamond powder (commercially available from        company Carbodeon), referred as nanodiamond powder A.    -   Nanodiamond powder from Heyuan ZhongLian Nanotechnology Co.,        Ltd, referred as nanodiamond powder B.

Solvents:

N-Methyl-2-pyrrolidone (NMP), Assay≥99.5%, was purchased from VWRChemicals/Prolabo, Assay≥99.5%.

1-Ethyl-2-pyrrolidone (NEP), Assay≥98%, was purchased from AppliChemPanreac.

γ-Butyrolactone (GBL), Assay≥99%, was purchased from Sigma Aldrich.

Ethylene glycol (EG), Normapur, Assay 99.9%, was purchased from VWRProlabo.

The solvent based nanodiamond dispersion moisture contents weredetermined by Karl Fischer method at Ketek Oy, Finland.

The EDX analyses were carried out with Zeiss Ultra Plus Gemine tool. Theapplied acceleration voltage was 20 kV.

The XRD patterns were recorded between angles 5-45° (2Theta) by usingPhilips Powder X-Ray Diffractometer by using MoKα-radiation (Kat0.70932A) with fixed divergence slit (size 0.8059c), but with outincident beam mono-chromator. Power of radiation was 1757 W. Theanalyses were conducted by VTT, Finland.

Nanodiamond Hydrogenation

Hydrogenation at 500° C.

16.63 g (sample A), 17.59 g (sample B), 17.63 g (sample C) and 17.58 g(sample D) of nanodiamond powder A were loaded on alumina crucibles asshown FIG. 1. Gas change was conducted in single step, for the firstvery careful pumping vacuum down to 10⁻¹ mbar and then introducing 4%hydrogen gas (purity of hydrogen gas 99.9999%) in argon. The hydrogencontaining argon gas flow was adjusted to 200 ml/min.

As reaching treatment temperature of 500° C., the samples were keptunder said gas flow for 6 hours time, followed by gradual cooling ofreaction furnace into room temperature, within 14 hours time. Thetreatment temperature plot is depicted in FIG. 2. The resultinghydrogenated nanodiamond powder exhibits paler colour than untreatednanodiamond powder A. The untreated and hydrogenated samples are shownin FIGS. 3a and 3b . The powder was collected and weighted and the yieldwas measured to 97.4%.

A 0.5 g sample of hydrogenated nanodiamond powder was mixed into 100 mlof deionized water, and the resulting mixture was subjected toultrasonic treatment for one hour time. The resulting suspension D50particle size distribution was measured to 302 nm, and zeta potential to+52.0 mV.

Hydrogenation at 520° C.

25.68 g of nanodiamond powder A and 23.74 g of nanodiamond powder B wereloaded on two alumina crucibles. Gas change was conducted in singlestep, for the first very careful pumping vacuum down to 10⁻¹ mbar andthen introducing 4% hydrogen gas (purity of hydrogen gas 99.9999%) inargon. The hydrogen containing argon gas flow was adjusted to 200ml/min. As reaching treatment temperature of 520° C., the samples werekept under said gas flow for 6 hours time, followed by gradual coolingof reaction furnace into room temperature, within 14 hours time. Alsohere, the resulting hydrogenated nanodiamond powders exhibits palercolour than untreated nanodiamond powders. The powders were collectedand weighted and the yield was measured to 95.8% for nanodiamond powderA and 93.4 for nanodiamond powder B.

A 0.5 g sample of hydrogenated nanodiamond B powder was mixed into 100ml of deionized water, and the resulting mixture was subjected toultrasonic treatment for one hour time. The resulting suspension zetapotential was measured to +68.4 mV.

Hydrogenation at 600° C.

20.00 g, 20.00 g, 20.00 g and 20.00 g of nanodiamond powder B wereloaded on alumina crucibles. Gas change was conducted in single step,for the first very careful pumping vacuum down to 10⁻¹ mbar and thenintroducing 4% hydrogen gas (99.9999%) in argon. The hydrogen containingargon gas flow was adjusted to 200 ml/min. As reaching treatmenttemperature of 600° C., the samples were kept under said gas flow for 6hours time, followed by gradual cooling of reaction furnace into roomtemperature, within 14 hours time. Also here, the resulting hydrogenatednanodiamond powder exhibits paler colour than untreated nanodiamondpowder B. The powders were collected and combined. The combined samplewas weighted and the yield was measured to 92.2%.

The EDX analysis revealed the produced hydrogen terminated nanodiamondpowder is essentially free of nitrogen contained surface functions.

The XRD analysis revealed there is hardly any graphitic carbon presentin produced hydrogenated nanodiamond powder. The area ratio forGraf.(002)/Diam.(111) for the produced hydrogenated nanodiamond powderwas determined to be 0.01 whilst it was 0.09 for the applied startingmaterial nanodiamond powder. The nanodiamond crystal size (111) wasmeasured to be 31-33 Å.

A 0.5 g sample of hydrogenated dispersion was mixed into 100 ml ofdeionized water, and the resulting mixture was subjected to ultrasonictreatment for one hour time. The resulting suspension zeta potential wasmeasured to +60.2 mV. The sample zeta potential curve is shown in FIG.4.

Beads Assisted Sonic Disintergration of Hydrogenated Nanodiamond BPowder Sample (Hydrogenated at 600° C.)

312.5 g of deionized water and 7.5 g of zeta positive hydrogenatednanodiamond powder B were mixed with a conventional magnetic stirrer toform a nanodiamond suspension. The suspension was subjected toultrasonic treatment for 30 minutes, using H14 blade and 40% amplitude.The suspension was stirred with conventional magnetic stirrer (100 rpm),with simultaneous cooling with an ice-bath.

Said suspension was then subjected to beads assisted sonicdisintergration, using 30 micron zirconia beads. The milling speed wasadjusted to 3700 rpm, and after 20 minutes treatment time, theultrasonic power was lowered to cycle 0.7 from 0.5. The rotation pumpspeed was maintained at 10% throughout the two hours processing time. Asthe mill had been pre-filled with 180 ml of water, a total volume of 500ml of 1.5 wt-% highly zeta positive hydrogenated nanodiamond dispersionwas collected. The dispersion pH was measured to 6.4 and the zetapotential to +61.2 mV. The particle size distribution was the following:D10 3.16 nm; D50 5.81 nm; and D90 9.78 nm (FIG. 5).

The produced hydrogenated nanodiamond dispersion was dried and subjectedto thermogravimetric analysis (TGA). Almost linear TGA curve after 100′C(after water vaporization) indicates very stable oxidation ofnanodiamond material and thus, indicating very low surface nitrogen andoxygen levels. The dried hydrogenated nanodiamond dispersion TGA curveis depicted in FIG. 8.

Highly Zeta Positive Single Digit Aqueous Nanodiamond Dispersion ZetaPotential Stability and Tunability Within pH Range of 1.4 to 12.1

Nanodiamond powder B was subjected to 6 hours hydrogenation at 600° C.,followed by beads assisted sonic disintergration into 1.5 wt-% singledigit hydrogenated nanodiamond dispersion. In Table 1 are disclosedmeasured zeta potentials of single digit hydrogenated nanodiamonddispersion at pH range from 1.4 to 12.1. pH of the dispersion wascontrolled with either HCl or NaH₄OH and treated with sonication for 30min. The zeta potentials were measured from diluted 0.1 wt-% nanodiamondsamples. This zeta positive single digit hydrogenated nanodiamonddispersion sample was dispersion stable within pH range from 3 to 9.6,and retained of zeta potential of +30 mV or higher within pH range of1.9 to 9.8.

TABLE 1 Zeta potentials of single digit hydrogenated nanodiamonddispersion. zeta potential pH (mV) 1.4 27.0 2.2 48.6 3.1 47.7 4.1 50.95.0 56.4 6.1 57.6 7.4 50.0 8.9 42.3 9.3 35.0 9.6 30.9 11.0 9.4 11.8 10.412.1 11.9

The dispersion stability of pH adjusted hydrogenated nanodiamonddispersion samples within pH range of 1.4 to 12.1 is featured in FIG. 6.

Beads Assisted Sonic Disintergration of Hydrogenated Nanodiamond BPowder Sample (Hydrogenated at 500° C.)

312.5 g of deionized water and 17.5 g of zeta positive hydrogenatednanodiamond powder B were mixed with a conventional magnetic stirrer toform a nanodiamond suspension. The suspension was subjected toultrasonic treatment for 30 minutes, using H14 blade and 40% amplitude.The suspension was stirred with conventional magnetic stirrer (100 rpm),with simultaneous cooling with an ice-bath.

Said suspension was then subjected to beads assisted sonicdisintergration, using 30 micron zirconia beads. The milling speed wasadjusted to 3700 rpm, and after 20 minutes treatment time, theultrasonic power was lowered to cycle 0.7 from 0.5. The rotation pumpspeed was maintained at 10% throughout the two hours processing time. Asthe mill had been pre-filled with 180 ml of water, a total volume of 500ml of 3.5 wt-% highly zeta positive hydrogenated nanodiamond dispersionwas collected. The dispersion pH was measured to 6.6 and the zetapotential to +54.6 mV. The particle size distribution was the following:D10 3.97 nm; D50 6.33 nm; and D90 10.9 nm (FIG. 7).

Preparation of Highly Zeta Positive 3.0 wt. % Single Digit HydrogenatedNanodiamond Dispersion in NMP

The evaporator water bath was preheated up to 45° C. 36.5 g of 2.74 wt.% aqueous highly zeta positive, hydrogen functionalized nanodiamonddispersion was weighted into 250 ml round bottomed flask, followed byaddition of 33 g of NMP solvent. The resulting mixture was stirrervigorously for 5 minutes time. Then, the mixture was evaporated in thefollowing sequences: 1000 mbar down to 200 mbar (in three minutes), downto 100 mbar during additional one minute evaporation, down to 50 mbar instill another minute of evaporation, and to less than 15 mbar by 10minute total evaporation time. Said steps were carried out withoutplacing the flask into evaporator water bath. Thereafter, evaporationwas continued by placing the flask into water bath (T=45° C.), risingthe water bath temperature during 10 minutes to 60° C. Then, theevaporation was continued until reaching the total evaporation time of29 minutes.

The resulting dispersion was weighted to 33.2 g. Resulting dispersionwater content was measured to 1.46 wt. % by Karl Fischer titration. Theoven dried nanodiamond sample weighted 1.0 g, revealing that producedNMP based nanodiamond dispersion nanodiamond concentration is 3.0 wt. %

The dispersion exhibited the following particle size distribution: D10:1.94 nm; D50: 2.78 nm; D90: 4.38 nm. The dispersion zeta potential wasmeasured to +40.7 mV. The particle size distribution of preparedhydrogen functionalized nanodiamond dispersion is illustrated in FIG. 9.

It was also possible to prepare 4.2 wt. % hydrogen functionalizednanodiamond dispersion in NMP, with the following particle sizedistribution: D10: 1.80 nm; D50: 2.64 nm and D90: 4.37 nm. After coolingdown such a dispersion viscosity is increased as compared to 3 wt. %hydrogen functionalized nanodiamond dispersion.

Preparation of Highly Zeta Positive 2.0 wt. % Single Digit HydrogenatedNanodiamond Dispersion in NEP

The evaporator water bath was preheated up to 45° C. 42.0 g of 2.38 wt.% aqueous highly zeta positive, hydrogen functionalized nanodiamonddispersion was weighted into 250 ml round bottomed flask, followed byaddition of 50 g of NEP solvent. The resulting mixture was stirrervigorously for 5 minutes time. Then, the mixture was evaporated in thefollowing sequences: 1000 mbar down to 200 mbar (in three minutes), downto 100 mbar during additional one minute evaporation, down to 50 mbar instill another minute of evaporation, and to less than 15 mbar by 10minute total evaporation time. Said steps were carried out withoutplacing the flask into evaporator water bath. Thereafter, evaporationwas continued by placing the flask into water bath (T=45° C.), risingthe water bath temperature during 10 minutes to 60° C. Thereafter,evaporation was continued for additional 5 minutes at said temperature.

The resulting dispersion was weighted to 50.0 g. Resulting dispersionwater content was measured to 1.18 wt. % by Karl Fischer titration. Theoven dried nanodiamond sample weighted 1.0 g, revealing that producedNEP based nanodiamond dispersion nanodiamond concentration is 2.0 wt. %

The prepared dispersion exhibited the following particle sizedistribution: D10: 2.21 nm; D50: 4.71 nm and D90: 8.21 nm. The particlesize distribution curve is illustrated in FIG. 10. The dispersion zetapotential was measured to 55.1 mV.

Preparation of Highly Zeta Positive 3.1 wt. % Single Digit HydrogenatedNanodiamond Dispersion in Gamma-Butyrolactone (GBL)

The evaporator water bath was preheated up to 45° C. 36.5 g of 2.74 wt.% aqueous highly zeta positive, hydrogen functionalized nanodiamonddispersion was weighted into 250 ml round bottomed flask, followed byaddition of 33 g of GBL solvent. The resulting mixture was stirrervigorously for 5 minutes time. Then, the mixture was evaporated in thefollowing sequences: 1000 mbar down to 200 mbar (in three minutes), downto 100 mbar during additional one minute evaporation, down to 50 mbar instill another minute of evaporation, and to less than 15 mbar by 10minute total evaporation time. Said steps were carried out withoutplacing the flask into evaporator water bath. Thereafter, evaporationwas continued by placing the flask into water bath (T=45° C.), risingthe water bath temperature during 7 minutes to 60° C. Then, theevaporation was continued for additional 8 minutes.

The resulting dispersion was weighted to 32.2 g. Resulting dispersionwater content was measured to 0.23 wt. % by Karl Fischer titration. Theoven dried nanodiamond sample weighted into 1.0 g, revealing thatproduced GBL based nanodiamond dispersion nanodiamond concentration is3.1 wt. %

The prepared dispersion exhibited the following particle sizedistribution: D10: 0.844 nm; D50: 1.77 nm; D90: 2.75 nm. The particlesize distribution curve is illustrated in FIG. 11. The dispersion zetapotential was measured to 61.8 mV.

It was also possible to prepare 4.1 wt. % hydrogen functionalizednanodiamond dispersion in GBL, with the following particle sizedistribution: D10: 1.16 nm; D50: 1.82 nm and D90: 2.75 nm. Further, ifwas possible to prepare a 5.0 wt. % hydrogen functionalized nanodiamonddispersion in GBL, with the following particle size distribution: D10:1.05 nm; D50: 1.65 nm and D90: 2.67 nm. After cooling down saiddispersions, the 4.1 wt. % hydrogen functionalized nanodiamonddispersion exhibits slightly higher viscosity as compared tocorresponding 3.1 wt. % dispersion, the 5.0 wt. % dispersion being high.

Preparation of Highly Zeta Positive 3.0 wt. % Single Digit HydrogenatedNanodiamond Dispersion in Ethylene Glycol (EG)

The evaporator water bath was preheated up to 65° C. 126.0 g of 2.38 wt.% aqueous highly zeta positive, hydrogen functionalized nanodiamonddispersion was weighted into one liter round bottomed flask, followed byaddition of 100 g of EG solvent. The resulting mixture was stirrervigorously for 5 minutes time. Then, the mixture was evaporated in thefollowing sequences: 1000 mbar down to 200 mbar (in three minutes), downto 100 mbar during additional one minute evaporation, down to 60 mbar instill another minute of evaporation, and to 20 mbar by 7 minute totalevaporation time. Said steps were carried out without placing the flaskinto evaporator water bath. Thereafter, evaporation was continued byplacing the flask into water bath (T=65° C.), rising the water bathtemperature during 10 minutes to 80° C. Then, the evaporation wascontinued for additional 7 minutes.

The resulting dispersion was weighted to 98.7 g. Resulting dispersionwater content was measured to 0.71 wt. % by Karl Fischer titration. Theoven dried nanodiamond sample weighted into 3.0 g, revealing thatproduced EG based nanodiamond dispersion nanodiamond concentration is3.0 wt. %

The prepared dispersion exhibited the following particle sizedistribution: D10: 0.749 nm; D50: 1.32 nm and D90: 2.34 nm. The particlesize distribution curve is illustrated in FIG. 12. It was impossible todetermine the produced dispersion zeta potential value accurately, butit carried a positive charge.

Preparation of Highly Zeta Positive 5.0 wt. % Single Digit HydrogenatedNanodiamond Dispersion in Ethylene Glycol (EG)

The evaporator water bath was preheated up to 65° C. 36.5 g of 2.74 wt.% aqueous highly zeta positive, hydrogen functionalized nanodiamonddispersion was weighted into one liter round bottomed flask, followed byaddition of 20 g of EG solvent. The resulting mixture was stirrervigorously for 5 minutes time. Then, the mixture was evaporated in thefollowing sequences: 1000 mbar down to 200 mbar (in two minutes), downto 100 mbar during additional 1.5 minutes evaporation, down to 40 mbarin still another minute of evaporation, and to 18 mbar by 7 minute totalevaporation time. Said steps were carried out without placing the flaskinto evaporator water bath. Thereafter, evaporation was continued byplacing the flask into water bath (T=65° C.), rising the water bathtemperature during 10 minutes to 80° C. Then, the evaporation wascontinued for additional 1 minute.

The resulting dispersion was weighted to 19.9 g. The oven driednanodiamond sample weighted into 1.0 g, revealing that produced EG basednanodiamond dispersion nanodiamond concentration is 5.0 wt. %

The prepared dispersion exhibited the following particle sizedistribution: D10: 0.825 nm; D50: 1.52 nm and D90: 2.34 nm. The particlesize distribution curve is illustrated in FIG. 13. It was impossible todetermine the produced dispersion zeta potential value accurately, butit carried a positive charge.

1. A method for producing zeta positive hydrogenated nanodiamond powdercomprising heating nanodiamond particles under a gas atmospherecomprising hydrogen gas at substantially ambient pressure, whereinhydrogen gas content in the gas atmosphere is 1-10%.
 2. The methodaccording to claim 1, wherein the gas atmosphere additionally comprisesone or more inert gases.
 3. The method according to claim 2, wherein theinert gas is selected from the group consisting of argon, nitrogen,helium, or a mixture thereof, preferably argon.
 4. The method accordingto any one of claims 1-3, wherein hydrogen gas content in the gasatmosphere is 2-8%, preferably 3-7%.
 5. The method according to any oneof claims 1-4, wherein the nanodiamond particles are heated for from 1to 15 hours, preferably from 2 to 10 hours, and more preferably from 3to 9 hours.
 6. The method according to any one of claims 1-5, whereinthe nanodiamond particles are heated at a temperature from 300 to 1000°C., preferably from 400 to 900° C., and more preferably from 400 to 850°C.
 7. A method for producing zeta positive single digit hydrogenatednanodiamond dispersion comprising i) heating nanodiamond particles undera gas atmosphere comprising hydrogen gas at substantially ambientpressure for producing zeta positive hydrogenated nanodiamond powder,wherein hydrogen gas content in the gas atmosphere is 1-10%; ii)suspending the zeta positive hydrogenated nanodiamond powder into aliquid medium; and iii) subjecting the zeta positive hydrogenatednanodiamond suspension to beads assisted sonic disintergration.
 8. Themethod according to claim 7, wherein in step i) the gas atmosphereadditionally comprises one or more inert gases.
 9. The method accordingto claim 8, wherein in step i) the inert gas is selected from the groupconsisting of argon, nitrogen, helium, or a mixture thereof, preferablyargon.
 10. The method according to any one of claims 7-9, wherein instep i) hydrogen gas content in the gas atmosphere is 2-8%, preferably3-7%.
 11. The method according to any one of claims 7-10, wherein instep i) the nanodiamond particles are heated for from 1 to 15 hours,preferably from 2 to 10 hours, and more preferably from 3 to 9 hours.12. The method according to any one of claims 7-11, wherein in step i)the nanodiamond particles are heated at a temperature from 300 to 1000°C., preferably from 400 to 900° C., and more preferably from 400 to 850°C.
 13. The method according to claim 7-12, wherein the liquid medium isselected from the group consisting of polar protic solvents, polaraprotic solvents, dipolar aprotic solvents, aromatic solvents,chlorinated solvents, ionic liquids, or a mixture of the solvents. 14.The method according to claim 13, wherein the polar protic solvent iswater, alcohol, linear aliphatic diol, branched diol or carboxylic acid;the polar aprotic solvent is tetrahydrofuran, propylene carbonate orlactam; the dipolar aprotic solvent is ketone, ester,N,N-methylformamide or dimethyl sulfoxide; the aromatic solvent istoluene, xylenes or benzene; the chlorinated solvent is dichloromethane,trichloroethylene or chloroform; and the ionic liquid is1-ethyl-3-methylmidazolium chloride, 1-butyl-3-methylmidazoliumchloride, 1-ethyl-3-methyl-imidazolium ethylsulfate, 1-ethyl-3-methylimidazolium diethylphosphate, 1-ethyl-3-methyl-imidazolium dicyanamide,tris-(2-hydroxy-ethyl)-methylammonium methylsulfate,1-ethyl-3-methyl-imidazolium thiocyanate, 1-ethyl-3-methyl-imidazoliumtetrafluoroborate, 1-ethyl-3-methyl-imidazoliumtrifluoromethanesulfonate, 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methyl-imidazoliummethylcarbonate and 1-butyl-3-methyl-imidazolium methylcarbonate. 15.The method according to any one of claims 7-14, wherein the liquidmedium is selected from the group consisting of water, methanol,ethanol, isopropanol, linear aliphatic diols, branched diols,N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP) and dimethylsulfoxide (DMSO), or a mixture of any said solvents, preferably theliquid medium is water.
 16. The method according to any one of claims7-15, wherein zeta potential of the zeta positive single digithydrogenated nanodiamond dispersion is over +35 mV, preferably over +40mV, and most preferably over +50 mV measured at pH higher than
 7. 17.The method according to any one of claims 7-16, wherein zeta potentialof the zeta positive single digit hydrogenated nanodiamond dispersion isover +50 mV, preferably over +60 mV measured at pH lower than or
 7. 18.The method according to any one of claims 7-17, wherein D90 averageparticle size distribution of the zeta positive single digithydrogenated nanodiamond dispersion is from 2 nm to 30 nm, preferablyfrom 2 nm to 20 nm, more preferably from 2 to 14 nm, and most preferablyfrom 3 nm to 12 nm.
 19. The method according to any one of claims 7-18,wherein the zeta positive single digit hydrogenated nanodiamond particleconcentration in the dispersion is at least 0.2 wt-%, preferably between0.2 and 10 wt-%, and more preferably between 0.5 and 8 wt-%.
 20. A zetapositive hydrogenated nanodiamond powder comprising zeta positivehydrogenated nanodiamond particles, wherein i) zeta potential of thezeta positive hydrogenated nanodiamond particles as suspended in wateris over +30 mV measured at pH higher than 7, ii) D50 average particlesize distribution of the zeta positive hydrogenated nanodiamondparticles is from 2 nm to 400 nm when subjected to one hour ultrasonictreatment in water.
 21. The zeta positive hydrogenated nanodiamondpowder according to claim 20, wherein the zeta potential of the zetapositive hydrogenated nanodiamond particles suspended in water is over+40 mV, more preferably over +50 mV, and most preferably over +60 mVmeasured at pH higher than
 7. 22. The zeta positive hydrogenatednanodiamond powder according to claim 20 or 21, wherein the zetapotential of the zeta positive hydrogenated nanodiamond particlessuspended in water is over +30 mV at a pH-range from 1.5 to 13,preferably at a pH-range from 2 to 11, and more preferably at a pH-rangefrom 2 to
 10. 23. Zeta positive single digit hydrogenated nanodiamonddispersion comprising zeta positive single digit hydrogenatednanodiamond particles and a liquid medium, wherein i) zeta potential ofthe zeta positive single digit hydrogenated nanodiamond dispersion isover +30 mV measured at pH higher than 7, ii) D90 average particle sizedistribution of the zeta positive single digit hydrogenated nanodiamondparticles in the dispersion is from 2 nm to 12 nm.
 24. The zeta positivesingle digit hydrogenated nanodiamond dispersion according to claim 23,wherein the zeta potential of the zeta positive single digithydrogenated nanodiamond dispersion is over +40 mV, more preferably over+50 mV, and most preferably over +60 mV, measured at pH higher than 7.25. The zeta positive single digit hydrogenated nanodiamond dispersionaccording to claim 23 or 24, wherein the zeta potential of the zetapositive single digit hydrogenated nanodiamond dispersion is over +60mV, and preferably over +70 mV measured at pH lower than or
 7. 26. Thezeta positive single digit hydrogenated nanodiamond dispersion accordingto any of claims 23-25, wherein the zeta negative single digithydrogenated nanodiamond particle concentration in the dispersion is atleast 0.2 wt-%, preferably between 0.2 and 10 wt-%, and more preferablybetween 0.5 and 8 wt-%.
 27. The zeta positive single digit hydrogenatednanodiamond dispersion according to any one of claims 23-26, wherein theliquid medium is selected from the group consisting of polar proticsolvents, polar aprotic solvents, dipolar aprotic solvents, aromaticsolvents, chlorinated solvents, ionic liquids, or a mixture of thesolvents.
 28. The zeta positive single digit hydrogenated nanodiamonddispersion according to claim 27, wherein the polar protic solvent iswater, alcohol, linear aliphatic diol, branched diol or carboxylic acid;the polar aprotic solvent is tetrahydrofuran, propylene carbonate orlactam; the dipolar aprotic solvent is ketone, ester,N,N-methylformamide or dimethyl sulfoxide; the aromatic solvent istoluene, xylenes or benzene; the chlorinated solvent is dichloromethane,tri-chloroethylene or chloroform; and the ionic liquid is1-ethyl-3-methylmidazolium chloride, 1-butyl-3-methylmidazoliumchloride, 1-ethyl-3-methyl-imidazolium ethylsulfate, 1-ethyl-3-methylimidazolium diethylphosphate, 1-ethyl-3-methyl-imidazolium dicyanamide,tris-(2-hydroxyethyl)-methylammonium methylsulfate,1-ethyl-3-methyl-imidazolium thiocyanate, 1-ethyl-3-methyl-imidazoliumtetrafluoroborate, 1-ethyl-3-methyl-imidazolium trifluoromethasulfonate,1-ethyl-3-methyl-imidazolium bis (trifluoromethanesulfonyl)imide,1-ethyl-3-methyl-imidazolium methylcarbonate and1-butyl-3-methyl-imidazolium methyl-carbonate.
 29. The zeta positivesingle digit hydrogenated nanodiamond dispersion according to any one ofclaims 23-28, wherein the liquid medium is selected from the groupconsisting of water, methanol, ethanol, iso-propanol, linear aliphaticdiols, branched diols, N-methyl-2-pyrrolidone (NMP),N-ethyl-2-pyrrolidone (NEP) and dimethyl sulfoxide (DMSO), or a mixtureof any said solvents, preferably the liquid medium is water.
 30. Thezeta positive single digit hydrogenated nanodiamond dispersion accordingto any one of claims 23-29, wherein the D90 average particle sizedistribution of the zeta positive single digit hydrogenated nanodiamondparticles is from 3 nm to 12 nm.
 31. The zeta positive single digithydrogenated nanodiamond dispersion according to any one of claims23-30, wherein pH of the zeta positive single digit hydrogenatednanodiamond dispersion is 1.5 to 13, preferably from 1.5 to 12, morepreferably from 2 to 10.